1. Field of the Invention
The present invention relates to an image forming method.
2. Description of the Related Art
Inkjet recording apparatuses, which have a simple configuration, can provide high-quality images through inkjet recording. In order to be desirably ejected from inkjet heads, inkjet inks are produced so as to have a viscosity of several mPa·s to about 30 mPa·s and a surface tension of about 20 mN/m to about 40 mN/m.
For producing an ink with a viscosity falling within the above range, the amount of an ink solvent is generally adjusted to 50% by mass to 90% by mass. Examples of the ink solvent used include water, organic solvents, oils and photopolymerizable monomers. Among them, water is often used from the viewpoint of giving less environmental load. Also, a high-boiling-point solvent (e.g., glycerin) is generally incorporated into the ink solvent so that the formed ink is prevented from drying to avoid clogging of ejection nozzles of the inkjet head.
When an ink containing a large amount of solvent is printed on a recording medium, the printed product involves image bleeding and color mixing. In view of this, recording media are provided with a solvent-absorbing layer (ink-receiving layer) having a thickness of about 20 μm to about 30 μm, and the obtained recording media are used as a paper sheet specialized for inkjet recording (FIG. 5) to prevent the occurrence of such unfavorable phenomena (i.e., image bleeding and color mixing).
In general, when an aqueous ink is used for inkjet recording, water serving as a solvent thereof infiltrates into base paper to cause deformation; e.g., curling and cockling. However, when a recording medium used have such a laminated structure that solvent-absorbing layers 22 are formed on base paper 21 (FIG. 5), the solvent-absorbing layers prevent water from infiltrating into the base paper, resulting in avoiding such deformation.
In addition, in forming graphical images with a high image density and a high image area ratio, a larger amount of ink is applied on per unit area of the recording medium and thus, the ink-absorbing layer cannot completely prevent infiltration of the ink solvent into the base paper. In this case, water-resistant paper (e.g., laminated paper) is used which has a water-resistant layer formed of polyolefin, etc. (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 2005-238829 and 2005-96285).
Conventionally, inkjet recording techniques have been used in office printers and home printers. In recent years, they have also been being applied to the commercial printing field. This field requires not a printed product having a photo-like surface obtained by completely preventing infiltration of the ink solvent into the base paper, but a printed product having a texture like that obtained by printing generally used paper. Here, a recording medium having a solvent-absorbing layer with a thickness of 20 μm to 30 μm deteriorates the printed products in terms of, for example, surface glossiness, texture and stiffness. Thus, in the commercial printing field, the inkjet recording technique is merely applied, for example, to posters and ledger sheets in which degradation of the above properties is allowable. Also, use of a recording medium having a solvent-absorbing layer and/or a water-resistant layer leads to cost elevation, which is another cause of the above-described limited applications.
Some patent literatures disclose inkjet recording methods for forming high-quality images, where a separately provided liquid composition (reaction mixture) is applied onto a recording medium prior to jetting of inkjet ink (see, for example, JP-A Nos. 09-207424 and 2006-188045). In these methods, the liquid composition (treatment liquid) is applied onto the surface of recording media and then pigment ink is applied so that it is mixed with the treatment liquid in a liquid state. Such methods pose problems in that the fixing property of the formed images is degraded and the printed recording media involve deformation such as curling and cockling, which would not be observed in image formation using pigment ink alone.